11. Introduction
2
3rmnet driver is used for supporting the Multiplexing and aggregation
4Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm
5Technologies, Inc. modems.
6
7This driver can be used to register onto any physical network device in
8IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.
9
10Multiplexing allows for creation of logical netdevices (rmnet devices) to
11handle multiple private data networks (PDN) like a default internet, tethering,
12multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends
13packets with MAP headers to rmnet. Based on the multiplexer id, rmnet
14routes to the appropriate PDN after removing the MAP header.
15
16Aggregation is required to achieve high data rates. This involves hardware
17sending aggregated bunch of MAP frames. rmnet driver will de-aggregate
18these MAP frames and send them to appropriate PDN's.
19
202. Packet format
21
22a. MAP packet (data / control)
23
24MAP header has the same endianness of the IP packet.
25
26Packet format -
27
28Bit             0             1           2-7      8 - 15           16 - 31
29Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length
30Bit            32 - x
31Function     Raw  Bytes
32
33Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
34or data packet. Control packet is used for transport level flow control. Data
35packets are standard IP packets.
36
37Reserved bits are usually zeroed out and to be ignored by receiver.
38
39Padding is number of bytes to be added for 4 byte alignment if required by
40hardware.
41
42Multiplexer ID is to indicate the PDN on which data has to be sent.
43
44Payload length includes the padding length but does not include MAP header
45length.
46
47b. MAP packet (command specific)
48
49Bit             0             1           2-7      8 - 15           16 - 31
50Function   Command         Reserved     Pad   Multiplexer ID    Payload length
51Bit          32 - 39        40 - 45    46 - 47       48 - 63
52Function   Command name    Reserved   Command Type   Reserved
53Bit          64 - 95
54Function   Transaction ID
55Bit          96 - 127
56Function   Command data
57
58Command 1 indicates disabling flow while 2 is enabling flow
59
60Command types -
610 for MAP command request
621 is to acknowledge the receipt of a command
632 is for unsupported commands
643 is for error during processing of commands
65
66c. Aggregation
67
68Aggregation is multiple MAP packets (can be data or command) delivered to
69rmnet in a single linear skb. rmnet will process the individual
70packets and either ACK the MAP command or deliver the IP packet to the
71network stack as needed
72
73MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....
74MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...
75
763. Userspace configuration
77
78rmnet userspace configuration is done through netlink library librmnetctl
79and command line utility rmnetcli. Utility is hosted in codeaurora forum git.
80The driver uses rtnl_link_ops for communication.
81
82https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl
83